Apparatus for fault detection for parallelly transmitted audio signals and apparatus for delay difference detection and adjustment for parallelly transmitted audio signals

ABSTRACT

Characteristic amounts in each small region of audio signals transmitted in the working system and the standby system are extracted by characteristic amount calculators  6 - 1, 6 - 2 . A characteristic amount comparator  7  compares the characteristic amounts and judges occurrence of a fault. Characteristic amount difference calculators  9 - 1, 9 - 2 , ∥D∥ comparator  10 , and faulty system judging unit  11  judges the system having a fault. Majority decision processor  12  and significance judging unit  13  enhance the reliability of the judgment. Delay difference of audio signals between systems is roughly detected by sub-sampling audio signals of two systems and comparing them, and then accurately detected without sub-sampling. Delay difference between audio signals is adjusted by the detected delay difference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for fault detection forparallelly transmitted audio signals and an apparatus for delaydifference detection and adjustment for parallelly transmitted audiosignals, and more particularly to an apparatus for fault detection forparallelly transmitted audio signals suitable for selective reception offault-free audio signal at reception side by transmitting a same audiosignal by dividing into two channels, and an apparatus for delaydifference detection and adjustment for parallelly transmitted audiosignals transmitted in two channels.

2. Description of the Related Art

Hitherto, in parallel transmission of television signals for the purposeof high reliability transmission, same video/audio signals aretransmitted by dividing into two channels, and either channel isselected and received at the reception side.

FIG. 6 is a block diagram showing such a conventional paralleltransmitting apparatus. The diagram shows only about the audio signal.The upper side in the diagram is supposed to be the working system, andthe lower side is the standby system, and the reception side manualswitch 3 is usually connected to select the working system. At thistime, the input audio signal is transmitted by way of encoder 1-1,working transmission line 4-1, decoder 2-1, and manual switch 3, andbecomes an output audio signal.

An inspector monitors the channel status of two systems at the receptionside, and when detecting an occurrence of a fault in the working system,the inspector switches the manual switch 3 to the standby side. As aresult, the input audio signal is transmitted by way of encoder 1-2,standby transmission line 4-2, decoder 2-2, and manual switch 3, and theaudio signal is received intermittently through a normal channel.

The present applicant has previously proposed a technique of minimizingthe fault time of output signal by automating switching to the normalchannel in the event of a fault occurring in the receiving circuitduring parallel transmission in the following patent reference 1. Atechnique for detecting and adjusting delay difference of video signalshas been proposed in the following patent reference 2.

[Patent reference 1] Japanese Patent Laid-Open (JP-A) No. 2000-350238

[Patent reference 2] Japanese Patent Laid-Open (JP-A) No. 2002-142131

If the inspector manually switches the switch to select a normal channelto receive video/audio signals intermittently, it takes too much timeuntil completion of switching to normal channel capable of receivingnormal audio signals, and switching without interruption is difficult,and moreover the audio signal may not be continued smoothly at the timeof switching due to delay and deviation of audio signals between twochannels.

The technique in patent reference 1 relates to video signals, and it isintended to switch to a normal channel by detecting fault in videosignals. It is based on the condition that images of two systemsentering the apparatus have been already matched in position on thescreen, being free from delay deviation between the images. However, ifthe images are normal, the audio only may be faulty. In the technique ofpatent reference 1, the switching toward the normal channel side is notperformed in such a case, and the audio signal remains defective.

In parallel transmission, in most cases, the two systems run differentroutes geometrically, and generally there is a delay difference betweenimages of two systems. The delay difference between images of twosystems can be adjusted in the technique of patent reference 2, but thisis intended to detect and adjust the delay difference of video signals.When each system comprises devices for compressing and decodingtelevision signals, video and audio signals are processed separately,and the processing timing may be deviated slightly, and if the delaydifference of video signal is adjusted, the delay difference of audiosignal is not adjusted, and a slight deviation may be left over.Therefore, in order to receive audio signals continuously and favorablyregardless of switching of systems, it is also required to adjust thedelay difference between audio signals in two systems.

SUMMARY OF THE INVENTION

It is hence an object of the invention to present an apparatus capableof detecting a fault in a real time even in the event of occurrence of afault in audio signal of one system in parallel transmission of audiosignals, thereby enabling to receive normal audio signals continuouslyby instantly switching from the faulty system to the normal system.

It is other object of the invention to present an apparatus capable offavorably detecting and adjusting the delay difference between audiosignals of two systems at the reception side in parallel transmission ofaudio signals.

In order to accomplish the object, the first feature of the presentinvention is that an apparatus for fault detection for parallellytransmitted audio signals, being an apparatus for fault detection forparallelly transmitted audio signals transmitted in channels of twosystems, comprises characteristic amount extracting means provided ineach system for extracting a characteristic amount in each small regionof audio signal of each system, characteristic amount comparing meansfor comparing the characteristic amounts extracted by the characteristicamount extracting means between the two systems, and judging means forjudging occurrence of a fault in each system on the basis of thecomparison result of the characteristic amount comparing means.

Also, the second feature of this invention is that an apparatus forfault detection for parallelly transmitted audio signals, being anapparatus for fault detection for parallelly transmitted audio signalstransmitted in channels of two systems comprises characteristic amountextracting means provided in each system for extracting a characteristicamount in each small region of audio signal of each system, calculatingmeans for calculating the difference between the characteristic amountin faulty region and characteristic amount in normal region in eachsystem if fault occurs in either system and faulty region by parallellytransmitted audio signals is evident, and faulty system judging meansfor judging the system to be faulty at the side with the greaterdifference calculated by the calculating means.

Also, third feature of the present invention is that the apparatus forfault detection for parallelly transmitted audio signals, wherein thefaulty system judging means finally judges by majority decision processby using plural judging results on the basis of the differencecalculated by the calculating means, and renders the judging result notsignificant when the difference calculated by the calculating means issmaller than a specified value.

Also, forth feature of the present invention is that the apparatus forfault detection for parallelly transmitted audio signals, furthercomprising silent and mute detecting means for detecting the audiosignal in small region whether silent or not, comparing the audiosignals of two systems, and detecting whether the silent state is due toa fault or not.

Also, fifth feature of the present invention is that the the apparatusfor fault detection for parallelly transmitted audio signals, furthercomprising silent and mute detecting means for detecting the audiosignal in small region whether silent or not, comparing the audiosignals of two systems, and detecting whether the silent state is due toa fault or not.

Also, sixth feature of the present invention is that the the apparatusfor fault detection for parallelly transmitted audio signals, furthercomprising converting means for converting the input audio signals byconverting property of monotonous increase or monotonous decrease, bykeeping or inverting the sign, increasing the absolute value in therelatively small area of the absolute value, or decreasing the absolutevalue in the relatively large area of absolute value.

Also, seventh feature of the present invention is that an apparatus fordelay difference detection and adjustment for parallelly transmittedaudio signals, being an apparatus for delay difference detection andadjustment between same audio signals transmitted in circuits of twosystems, comprises a memory provided in each system for receiving audiodata from each system, comparing means for mutually comparing outputs ofthe memories, control means for controlling the reading position of thememory depending on the output of the comparing means, detecting meansfor detecting the delay difference between audio signals of two systemon the basis of the comparison result of the comparing means and thereading position of the memory, and adjusting means for adjusting thedelay difference between audio signals of two system according to thedelay difference.

Also, eighth feature of the present invention is that the apparatus fordelay difference detection and adjustment for parallelly transmittedaudio signals, wherein the sample values of audio signals are input intothe memory as audio data, and the comparing means determines thedifference of sample values.

Also, ninth feature of the present invention is that the apparatus fordelay difference detection and adjustment for parallelly transmittedaudio signals, wherein sub-sampling means is provided before the memory,and the sub-sample values sent out from the sub-sampling means are inputinto the memory as audio data.

Also, tenth feature of the present invention is that the apparatus fordelay difference detection and adjustment for parallelly transmittedaudio signals, wherein a route for direct input of audio data and aroute for input as sub-sampled are provided at the input side of thememory, and the delay difference between audio signals of two systems isdetected in two steps, these are a step of input of sub-sampled audiodata into the memory and a successive step of input of direct data intothe memory.

Also, eleventh feature of the present invention is that the apparatusfor delay difference detection and adjustment for parallelly transmittedaudio signals, wherein the sub-sampling means has absolute calculatingand maximum selecting means, and determines the absolute value of databefore sub-sampling, and further determines the maximum value in thesub-sampled object block and sends out as the sub-sample value.

Also, twelfth feature of the present invention is that the the apparatusfor delay difference detection and adjustment for parallelly transmittedaudio signals, wherein the sub-sampling means has square calculating andmaximum selecting means, and determines the square value of data beforesub-sampling, and further determines the maximum value in thesub-sampled object block and sends out as the sub-sample value.

Also, thirteenth feature of the present invention is that the apparatusfor a delay difference detection and adjustment for parallellytransmitted audio signals, wherein the detecting means detects the delaydifference for minimizing the difference of audio data of two systems,and the control means determines the majority decision of plural timesof delay difference detected by the detecting means, and controls thereading position of the memory according to the result.

According to the apparatus of this invention for fault detection forparallelly transmitted audio signals, since occurrence of a fault ineither one of the two systems is judged by using the characteristicamount of each small region of audio signals in each system, it is lesslikely to be influenced by the coding noise and stable fault detectionis realized as compared with a method of directly comparing two audiosamples or the like.

Since the faulty system is judged on the basis of the difference ofcharacteristic amounts of neighboring small regions of audio signals ineach system, a stable detection is possible, regardless of quantity oftransmission errors, as compared with a method of comparing the valuesof characteristic amounts.

By using a plurality of judging results on the basis of the differenceof characteristic amounts of neighboring small regions of audio signalsin each system, the faulty system is finally judged by majoritydecision, and the reliability of determination is enhanced byconsidering insignificant the judging result on the basis of thedifference less than the specified amount of difference ofcharacteristic amounts.

By detecting whether the audio signal in small region is silent or not,and by detecting whether the silent state is due to fault or not bycomparing audio signals in two systems, it is possible to prevent errorin decision between silent state due to mute fault and other silentstate.

If the characteristic amount of audio signal is evidently abnormal, bydetecting it distinctively, the state can be promptly judged withoutcomparing the characteristic values mutually.

Moreover, a fault can be detected correctly by using a small audiosignal, by keeping or inverting the sign, increasing the absolute valuein the relatively small area of absolute value, converting the audiosignal in the relatively large area of the absolute value by conversioncharacteristic of monotonous increase or monotonous decrease of theabsolute value, and executing fault detection in the converted audiosignals.

According to the apparatus of this invention for delay differencedetection and adjustment for parallelly transmitted audio signals,memories are provided in each system, outputs of the memories arecompared, and hence delay difference (deviation) between these signalsby comparison of audio signals of two systems can be detected andadjusted easily. At this time, calculating the difference of samplevalues of audio signals of two systems, the memory reading position ofthe smallest difference is determined. This reading position is theposition of the highest coincidence of audio signals of two systems, andthe delay difference between audio signals of two systems can bedetected as the difference of the reading position.

By sub-sampling the data before putting into each memory, and putting alimited number of sample values into the memory, even if the delaydifference is great, the delay difference can be detected with a limitedmemory capacity. After delay difference detection by sub-sampling, bydetecting the delay difference without sub-sampling, the delaydifference can be detected correctly without increasing the memorycapacity.

As the sub-sample value, by using the maximum value in the sub-sampleobject block of the absolute value of each data, or the maximum value inthe sub-sample object block of the square value of each data, thewaveform of the original audio signal can be expressed sufficiently by asmall number of samples. By mutually comparing them, a large delaydifference can be detected with a limited memory capacity.

Instead of detecting the delay difference for minimizing the differenceof two systems by mutually comparing the outputs of memories, and usingthe detected delay difference directly in adjustment, by determining themajority decision of plural times of detected delay difference, and byusing this result in adjustment as final delay difference amount, it isfree from effects of compression noise superposed in the audio signal orthe drift included in the detected delay difference, so that delaydifference can be detected and adjusted stably and accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a preferred embodiment of apparatus ofthe invention for fault detection for parallelly transmitted audiosignals;

FIG. 2 is a diagram showing an example of conversion characteristic ofsignal logarithmic conversion processor;

FIG. 3 is a waveform diagram for explaining the operation of signalcharacteristic amount calculator and characteristic amount comparator;

FIG. 4 is a waveform diagram for explaining the operation of faultysystem judging unit;

FIG. 5 is a waveform diagram showing an example of audio signalincluding a faulty region due to a fault;

FIG. 6 is a block diagram of a conventional parallel transmissionapparatus;

FIG. 7 is a block diagram showing a schematic configuration of apparatusof the invention for delay difference detection and adjustment forparallelly transmitted audio signals;

FIG. 8 is a block diagram of configuration example of delay differencedetector;

FIG. 9 is a block diagram of a configuration example of a sub-samplingunit;

FIG. 10 is a block diagram of a configuration example of a comparator;and

FIG. 11 is a waveform diagram showing the mode of vibration waveform ofaudio signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is specifically described below by referring to theaccompanying drawings. First, an apparatus for fault detection forparallelly transmitted audio signals is explained. FIG. 1 is a blockdiagram showing a preferred embodiment of apparatus of the invention forfault detection for parallelly transmitted audio signals. First, audiosignals are distributed into two channels by a distributor (not shown).Each of the channels is respectively transmitted through either aworking system or a standby system. When transmitting the audio signalby digitally compressing and encoding, each system includes encoders1-1, 1-2, and decoders 2-1, 2-2.

Supposing the upper side in the diagram to be the working system (systemA), and the lower side to be the standby system (system B), the manualswitch 3 of the reception side is usually connected to select theworking system. At this time, the audio signal is transmitted by way ofencoder 1-1, working transmission line 4-1, decoder 2-1, and manualswitch 3, and becomes an output audio signal.

When a fault occurs in the working system, the manual switch 3 isswitched to select the standby side according to the fault detectiondescribed blow. As a result, the audio signal is transmitted via encoder1-2, standby transmission line 4-2, decoder 2-2, and manual switch 3.

Fault detection of audio signal is described below. First, audio signalsof two systems A, B received at the reception side are put into signallogarithmic conversion processors 5-1, 5-2, respectively. The signallogarithmic conversion processors 5-1, 5-2 convert the input audiosignals into logarithm while saving their signs.

The human aural characteristic has a nonlinear feature capable ofsensibly distinguishing a signal even if its level is small, and signalprocessing is preferred to be conforming to this characteristic. Thesignal logarithmic conversion processors 5-1, 5-2 have the conversioncharacteristic satisfying this requirement, and the signal change insmall area of audio signals can be converted into a large change by thisconversion, so that fault detection characteristic of small voice can beimproved.

FIG. 2 shows an example of conversion characteristics of signallogarithmic conversion processors 5-1, 5-2. In this conversioncharacteristic, the relation of input signal s and output signal t isexpressed in the following formula (1).

$\begin{matrix}{t = \{ \begin{matrix}{1000\mspace{14mu}{\log_{10}( {s + 1} )}} & {{if}{\mspace{14mu}\;}( {s > 0} )} \\0 & {{if}{\mspace{14mu}\;}( {s = 0} )} \\{{- 1000}\mspace{14mu}{\log_{10}( {{- s} + 1} )}} & {{if}{\mspace{14mu}\;}( {s < 0} )}\end{matrix} } & (1)\end{matrix}$

The example in FIG. 2 shows a conversion characteristic of monotonousincrease (rightward rise) of logarithmic conversion while keeping thesign, but by inverting the sign, it is also possible to use theconversion characteristic of monotonous decrease (rightward fall). Inshort, for the input audio signal, by keeping or inverting the sign, theconversion characteristic may be either monotonous increase ormonotonous decrease for increasing the absolute value of the relativelysmall area of the absolute value or for decreasing the absolute value ofthe relatively large area of the absolute value.

Audio signals converted logarithmically in signal logarithmic conversionprocessors 5-1, 5-2 are put into signal characteristic amountcalculators 6-1, 6-2. The signal characteristic amount calculators 6-1,6-2 calculate and extract the characteristic amount of each small regionof audio signal. As the characteristic amount, the average or meandeviation of audio signal may be used, and plural types may beextracted.

Next, the extracted characteristic amount is put into a characteristicamount comparator 7, and the characteristic amounts are compared in eachsmall region between two systems A and B. If the difference incharacteristic amount between two systems A and B is less than aspecified threshold, it is judged that there is no fault in eithersystem in this region. On the other hand, if the difference incharacteristic amount between two systems A and B is more than aspecified threshold, it is judged that there is a certain fault ineither system in this region. On the basis of this judging result,whether normal region or faulty region can be determined, and normal orfaulty information is recorded in normal or faulty information recordingunit 8. The normal or faulty information is used when judging the faultysystem as described below.

FIG. 3 is a waveform diagram for explaining the operation of signalcharacteristic amount calculators 6-1, 6-2 and characteristic amountcomparator 7. First, the audio signal is divided into block (smallregion) units, for example, 1 block=128 samples. Next, in systems A, B,characteristic amounts in block are calculated and extracted. Thecharacteristic amount in block of systems A, B is expressed as{f_(A1)(p)}, {f_(B1)(p)} (i=1, 2, . . . , N) where p is block position.Herein, N denotes the number (types) of characteristic amounts to beextracted. As the characteristic amount, as mentioned above, variousvalues can be used such as average and standard deviation of audiosignals.

When the difference of characteristic values {f_(A1)(p)}, {f_(B1)(p)}between systems A and B is smaller than the specified threshold Th₁(that is, ^(∀)i→|f_(A1)(p)−f_(B1)(p)|≦Th₁), it is judged that no faulthas occurred in any system in this interval, and if the difference ismore than the specified threshold Th₁ (that is,

i→|f_(A1)(p)−f_(B1)(p)|>Th₁), it is judged that any fault has occurredin either system in this region. The judging result is recorded in thenormal or faulty information recorder 8 in each block as normal orfaulty information.

Thus, in the signal characteristic amount calculators 6-1, 6-2 andcharacteristic amount comparator 7, by utilizing a macroscopiccharacteristic amount hardly influenced by coding noise or the like, themagnitude of differential value of characteristic amounts betweensystems is used as the norm of fault detection. Therefore, when theencoder is inserted in two systems, generally, coding noise differs intwo systems, and this noise difference cause a problem in the faultdetection by a simple comparison of signals between two system, but inthis preferred embodiment, coding noise difference is not detectedfalsely as fault, and audio quality deterioration characteristic oftransmission error involving faulty area can be detected accurately.

The configuration of stages behind characteristic amount differencecalculators 9-1, 9-2 is explained. This configuration is intended tojudge the faulty system, that is, to detect which one of systems A, Bhas a fault. If the characteristic amount in each system presents anevidently abnormal value, meanwhile, the faulty system can be judged bythreshold comparators 14-1, 14-2, and silent and mute detector 15described below.

The characteristic amount difference calculators 9-1, 9-2 receive thecharacteristic amounts extracted in the signal characteristic amountcalculators 6-1, 6-2, and with referring to the normal or faultyinformation recorded in the normal or faulty information recorder 8,calculates the difference D of characteristic amounts between coincidingregion and non-coinciding region of the characteristic values betweensystem A and B, in each system.

A ∥D∥ comparator 10 compares the difference D of characteristic amountof system A and the difference D of characteristic amount of system B. Afaulty system judging unit 11 judges the faulty system on the basis ofresult of comparison of the ∥D∥ comparator 10. A large difference D ofcharacteristic amount means a large change of audio signal betweencoinciding region and non-coinciding region, and the possibility ofoccurrence of a fault is high. Further, depending on the degree ofdifference, the level of significance or non-significance of thejudgement is determined. Hence, the faulty system judging unit 11 judgescomprehensively in consideration of the above.

FIG. 4 is a waveform diagram showing the operation of the faulty systemjudging unit 11. The faulty system is judged in a plurality of blocks ofaudio signals, for example, in a unit of four (hereinafter, this iscalled a frame). Referring to the normal or faulty information recordedin the normal or faulty information recorder 8, the difference D={D_(i)}(i=1, 2, . . . N) of characteristic amount between coinciding region andnon-coinciding region of characteristic amounts between systems A and Bis calculated in each system, and the system with the greater value of Dis judged as faulty system. The judging result is issued in every frame.

Thus, in the faulty system judging unit 11, by positively utilizing thegeneral property of localizing of faulty region in transmission fault(this tendency is particularly strong in digital transmission fault), inthe event of a fault occurring in either system, and the site of faultis known in the parallelly transmitted audio signals, the magnitude ofdifference of characteristic amount in normal region and characteristicamount in faulty region in each system is used as the norm, and thesystem of the greater difference is judged to be a faulty system. Inthis case, since the system having fault is judged by detecting only thedifference of the characteristic amounts between normal region andfaulty region, it is possible to determine stably without depending onthe error rate of the system.

More specifically, first, in each characteristic amount, thedifferential absolute sum in the boundary area of normal and faultyregions is determined. Supposing the boundary of blocks in a frame to beb_(j) (j=1, 2, . . . , n), the function to express the position of twoblocks enclosing boundary b_(j) to be g₁(b_(j)), g₂(b_(j)), and thetotal boundaries of normal/faulty regions to be C, within-systemdifference D_(A1) of i-th characteristic amount in system A iscalculated in formula (2). Herein, n is the number of boundaries betweenblocks, and supposed to be 4 blocks per frame as shown in FIG. 4, thenumber of boundaries is 3. This is the same in system B.

$\begin{matrix}{D_{Ai} = {\sum\limits_{{bj} \in C}\;{{{f_{Ai}( {g_{1}( b_{j} )} )} - {f_{Ai}( {g_{2}( b_{j} )} )}}}}} & (2)\end{matrix}$

On the basis of within-system difference D₁ of characteristic amountcalculated in this manner, for example, ∥D∥ is calculated in formula(3), and the system with the greater value of ∥D∥ is determined to be afaulty system.∥D∥=max{wiDi}  (3)where W_(i) (i=1, 2, . . . , N) is the weighting coefficient of eachcharacteristic amount i, which can be determined as follows. Forexample, by executing a preliminary experiment using a fault-freesignal, distribution of differential values between the adjacent blocksis determined in each characteristic amount i, and the reciprocal numberof the standard deviation is obtained as the weight Wi for thecharacteristic amount i.

Using the judging result of the faulty system judging unit 11 as acontrol signal, when it shows a fault in the working system, the switch3 can be switched over to the standby system side. In this case, byoptimizing the types and number of characteristic amounts, it ispossible to switch to the standby system by raising the correctness rateof faulty system judgement, but misjudgment may occur even in this case.In this preferred embodiment, accordingly, the judging result of eachframe is collected plural times in a majority decision processor 12, anda final judgement is determined on the basis of the majority decision,thereby the reliability of judgement is enhanced.

Further, by comprising a significance judging unit 13, the judgingresult to be used in majority decision in the majority decisionprocessor 12 is limited only to the judging result determined to besignificant in formula (4), so that the efficacy of majority decisionprocessing can be further enhanced.

$\begin{matrix} {\frac{( {{D_{A}} - {D_{B}}} )}{{D_{A}} + {D_{B}}} > {TH}}arrow{{JUDGMENT}\mspace{14mu}{IS}\mspace{14mu}{SIGNIFICANT}}  & (4)\end{matrix}$

By majority decision processing according to the significancedetermination in formula (4), if the difference of characteristic amountdifference of system A and difference of characteristic amountdifference of system B is small, the reliability of the judging resultis judged to be small (not significant), and the result is not used inmajority decision.

The preferred embodiment further comprises threshold comparators 14-1,14-2 and silent and mute detector 15, and the characteristic amountscalculated by signal characteristic amount calculators 6-1, 6-2 andaudio signals are checked against predetermined conditions, and thechecking result is used in determination of faulty system or the levelof significance.

When the characteristic amounts calculated by signal characteristicamount calculators 6-1, 6-2 are evidently abnormal values, it is judgedthat a fault has occurred in the system showing abnormal values.Evidently abnormal values occur in the event of audio signals ofunusually high level, or adversely continued zero level signals. Thethreshold comparators 14-1, 14-2 provided in systems A and B detectabnormal values of characteristic amounts of systems A and B. The silentand mute detector 15 detects if abnormality of audio signal level hasoccurred only in one system or not. If the signal level of one systemcontinues to be zero, it is highly possible that mute fault has occurredin the encoder or decoder in a preceding stage of this system.

The faulty system judging unit 11 judges that fault has occurred in thesystem if the characteristic value or the signal level of one systemshows an abnormal value. When the characteristic value or signal levelshows an abnormal value, the judging result of the faulty system judgingunit 11 is regarded to have a high reliability, and the significancejudging unit 13 elevates the level of significance at this time.

FIG. 5 is a waveform showing an example of audio signal including faultyregion by fault. This diagram shows an audio signal waveform including afaulty region of extremely large signal level due to fault and a faultyregion by mute fault. As mentioned earlier, the faulty region due totransmission fault is localized.

Mute fault is, for example, output of silent signal (zero level signal)as a result of detection of transmission fault by encoder or decoderinstalled in a preceding stage of fault detection process. In such acase, if only one system is monitored, it cannot be distinguishedwhether the present audio signal is silent signal or has any mute fault.

In the preferred embodiment, the silent and mute detector 15 receivesaudio signals from both systems, and does not detect any fault if bothsystems are in silent state, and determines a mute fault when only onesystem is in silent state, and hence the reliability of fault detectionis high.

In the preferred embodiment, since the encoders and decoders areinstalled in both systems, and the audio signals are transmitted bydigital compression coding, but compression coding in transmission isnot always necessary, and the invention can be also applied in the caseof audio signal transmission without compression.

Next, the apparatus for delay difference detection and adjustment forparallelly transmitted audio signals is explained. FIG. 7 is a blockdiagram of configuration of apparatus for delay difference detection andadjustment for parallelly transmitted audio signals of the invention.Audio signals from channels of systems A and B are put respectively intoFIFO memories 71-A, 71-B. At the same time, these audio signals are alsoput into a delay difference detector 72.

In usual operation, for example, while system A is used in reception, aswitch 73 is switched to contact-a side, and the audio signal fromsystem A is sent out as output audio signal by way of FIFO memory 71-A.This means that system A is the working system, and system B is astandby system, and the switch 73 corresponds to the switch 3 in FIG. 1.In the event of fault occurring in system A, the switch 73 is switchedover to contact-b side, and this time the audio signal of system B issent out as output audio signal. This switching is done automaticallysame as in the publication in patent reference 1.

At the time of switching, in order to deliver the output audio signalwithout disruption, the delay difference detector 72 detects the delaydifference (deviation) between audio signals of systems A and B, andcontrols the relative reading positions of FIFO memories 71-A, 71-Baccording to this delay difference, and thereby adjusts the delay.

FIG. 8 is a block diagram of configuration of delay difference detector72. In the diagram, audio signals from channels of systems A and B areput into first memories (FIFO) 81-A, 81-B.

The first memories 81-A, 81-B can change the delay amount of audiosignals as their reading position is changed by FIFO controller 87described below. The first memories 81-A, 81-B have, for example, amemory capacity for 3 seconds each.

When the switches 83-A, 83-B are being switched to contact-a side, theaudio signals being read out from the first memories 81-A, 81-B aresub-sampled respectively in sub-sampling units 82-A, 82-B, andsub-sampled audio signals are put into second memories (RAM) 84-A, 84-Bas audio data. When the switches 83-A, 83-B are being switched tocontact-b side, the audio signals are directly put into second memories84-A, 84-B as audio data.

A comparator 85 randomly accesses the second memories 84-A, 84-B, andreads out audio data from them. The comparator 85 also compares the readaudio data while relatively changing the reading positions of the secondmemories 84-A, 84-B, and detects the difference of these audio data, andfinds the reading position corresponding to the minimum difference. Whenthe difference is minimum, the difference of reading positionscorresponds to the delay difference between audio signals of systems Aand B.

The detected delay difference is sent out to the FIFO controller 87 viaa majority decision processor 86. The FIFO controller 87 changes thereading positions of the first memories 81-A, 81-B according to theinput delay difference.

Next, the operation of the delay difference detector 72 is explained.Suppose the switches 83-A, 83-B are switched to the contact-a side. Atthis time, the audio signals of both systems A, B are put into firstmemories 81-A, 81-B, and the audio signals being read out from the firstmemories 81-A, 81-B are put into the second memories 84-A, 84-B as audiodata.

The comparator 85 reads out audio data from the second memories 84-A,84-B, and detects the difference of these audio data. This detection iscontinued while relatively changing the reading positions of the secondmemories 84-A, 84-B, and the difference of reading positionscorresponding to the minimum detected difference is obtained as thedelay difference between audio signals of systems A and B. This delaydifference is sent out to the FIFO controller 87 via the majoritydecision processor 86. The majority decision processor 86 is describedlater.

The FIFO controller 87 changes the reading positions of the firstmemories 81-A, 81-B according to the detected delay difference. Thedelay difference detected at this time is the result by sub-sampledaudio data, and hence this delay difference is multiplied by thesub-sampling rate to convert into the number of samples beforesub-sampling. For example, if the delay difference by 512 sub-samples (1sub-sample for 512 samples) is 10 sub-samples, by calculating 5120(=512×10) samples, and the reading positions of the first memories 81-A,81-B of systems A and B are changed. For example, if the result showsthe audio data of system A is 5120 samples behind, the reading positionsis delayed by 5120 samples from the first memory 81-B of system B.

Next, the switches 83-A, 83-Bare switched to the contact-b side. Theaudio signals newly read out from the first memories 81-A, 81-B aredirectly read into the second memories 84-A, 84-B this time withoutbeing sub-sampled.

The FIFO memory 87, same as above, changes the reading positions of thefirst memories 81-A, 81-B according to the delay difference betweenaudio signals of systems A and B detected by the comparator 85. In thiscase, some of the audio data put into the second memories 84-A, 84-B aresupplied directly without passing through the sub-sampling units 82-A,82-B, and the detected delay difference is directly applied in controlof reading positions of the first memories 81-A, 81-B.

When the detected delay difference is zero, the difference of thereading positions of the first memories 81-A, 81-B is the delaydifference between audio signals of systems A and B. According to thisdelay difference, the relative reading positions of the FIFO memories71-A, 71-B in FIG. 7 are controlled, and the delay difference betweenaudio signals of systems A and B is adjusted, which is not shown in thedrawing.

FIG. 9 is a block diagram of configuration of sub-sampling unit 82(82-A, 82-B). The sub-sampling unit 82 consists of an absolute valuecalculator 91, and a processor 92 for selection of maximum value in ablock.

The absolute value calculator 91 determines the absolute value of samplevalues of audio signals entered successively. The processor 92 forselection of maximum value in a block selects and sends out the maximumvalue in each 512 samples of the absolute value determined in theabsolute value detector 91, supposing the sub-sample object blocks tobe, for example, 512 samples.

In this way, first, the absolute value of sample values of audio signalin the sub-sample object block is determined, and the maximum of theabsolute values in the sub-sample object block is determined, andobtained as the sub-sample value representing the block, and hence thesub-sample value sufficiently representing the waveform of the originalaudio signal can be obtained.

FIG. 10 is a block diagram of configuration of comparator 85. A readingaddress generator 101 relatively changes the reading positions of thesecond memories 84-A, 84-B (FIG. 8), and reads out audio data from them.A subtractor 102, an absolute value calculator 103, and a cumulativeadder 104 read out, for example, 256 sub-samples each (or samples each)from the second memories 84-A, 84-B of systems A, B, and detects thedifferential absolute sum of these audio data.

A controller 105 processes this detection while relatively changing thereading positions of the second memories 84-A, 84-B, and determines thereading position when the minimum differential absolute sum is obtained.The difference of reading positions is the delay difference of audiosignals of systems A and B. This delay difference is transferred to theFIFO controller 87 in the later stage.

Thus, the delay difference of audio signals between systems A and B isdetected, but actually if the delay difference is once zero, the delaydifference may drift (delay difference of small value such as 1 or 2 maybe detected) due to difference in the coding noise superposed in audiosignals of systems A and B. That is, due to effects of coding noisedifferent in each system, a slight drift may be included in each resultof detection of delay difference.

This drift in delay difference is due to difference in coding noisesuperposed in audio signals in two systems, when audio signals of twosystems are separately transmitted after compression, being separatelycompressed at transmission side and decoded at reception side, and audiosignals of two system are received.

The majority decision processor 86 processes the detected delaydifference by majority decision to lessen the effect of such drift, andenables to detect and adjust the delay difference correctly. In themajority decision process, the largest delay difference among pluraldetected delay difference values should be sent out.

As explained herein, according to the apparatus of the invention fordelay difference detection and adjustment for parallelly transmittedaudio signals, since the outputs of memories disposed in each system arecompared mutually, it is easier to detect and adjust the delaydifference (deviation) of these audio data by comparison of audiosignals of two systems.

As in the preferred embodiment, by sub-sampling (thinning), convertingthe values, or processing by majority decision, detection and adjustmentof delay difference by comparison of sample values of audio signals oftwo systems in parallel transmission can be executed correctly andeasily even if the delay difference is large.

For example, in relay transmission of television signals by parallelcircuits, when the one system is satellite communication and othersystem is optical submarine cable communication, the transmission delaydifference of two systems may be very large. Sometimes, the delaydifference is as much as several seconds.

Digital audio signals are often sampled at 48 kHz, and a delaydifference of, for example, 3 seconds is converted into sample numberdifference, it is as much as 48000×3=144000 samples. Supposing 1 sampleto be 20 bits, it corresponds to 2880000 bits or about 3 Mbits.

To detect the delay difference between audio signals of two system, theaudio signals are once stored in memories, and while changing thereading positions, it is required to find the reading position of thesmallest difference between audio signals of two systems. However, if arandom access memory corresponding to 3 Mbits is prepared, and ifattempted to search all reading positions, the processing load isextremely heavy.

Accordingly, to save the memory capacity and lower the processing load,it is effective to sub-sample before putting into memories. That is,after obtaining an approximate delay difference in sub-sampled audiodata, and it is effective that the delay difference in the unit of onesample is detected again in a narrower searching range by audio data notsub-sampled. However, if the memory capacity is sufficient, the stage ofdelay difference detection by using sub-sampled audio data can beomitted.

The audio signal, unlike video signal, is usually a pulsation signalfrequently changing in plus and minus signs as shown in FIG. 11.Therefore, at the time of sub-sampling, if a sample is picked up atevery specific number of samples, the signal after sub-sampling may notalways represent the original waveform sufficiently.

To avoid such inconvenience, in the preferred embodiment, first theabsolute values of signals in sub-sample object block are determined,and the maximum value in the block is obtained as the sub-sample valuerepresenting this block.

The apparatus of the invention for delay difference detection andadjustment for parallelly transmitted audio signals is not limited tothis preferred embodiment alone, but may be changed and modifiedvariously within the technical scope thereof. For example, thesub-sampling means may have square calculation and maximum selectingmeans, and the square of the data before sub-sampling is determined, andthe maximum value in the sub-sample object block is determined, and sentout as sub-sample value.

The first memory is not always required, and the delay difference can bedetected on the basis of the reading position of the second memory. Bymajority decision process of detected delay difference, the effect ofdrift of delay difference is lessened, and stable and accurate detectionand adjustment of delay difference can be realized, but if the drift ofdetected delay difference is small, the majority decision process can beomitted.

As explained herein, according to the apparatus of the invention forfault detection for parallelly transmitted audio signals, the fault andfaulty system can be detected automatically in real time, and at highreliability, by using parallelly transmitted audio signals, whichcontributes to non-interruption of parallel transmission of audiosignals, that is, enhancement of reliability.

According to the apparatus of the invention for delay differencedetection and adjustment for parallelly transmitted audio signals, thedelay difference (deviation) of two systems can be detected and adjustedeasily, stably, and correctly by comparison of audio signals of twosystems.

1. An apparatus for fault detection for parallelly transmitted audiosignals, being an apparatus for fault detection for parallellytransmitted audio signals transmitted in channels of two systems,comprising: characteristic amount extracting means provided in eachsystem for extracting a characteristic amount in each small region ofeach audio signal of each system of said parallely transmitted audiosignals, characteristic amount comparing means for comparing thecharacteristic amounts extracted by the characteristic amount extractingmeans between the two systems, and judging means for judging occurrenceof a fault in each system on the basis of the comparison result of thecharacteristic amount comparing means for fault detection related toredundancy and reliability of the transmitted audio signals, wherein thetwo systems comprise a working system and a standby system and theworking system sends out the audio signal as an output audio signal inusual operation and, when the judging means judges the occurrence of afault in the working system, the standby system sends out the audiosignal as output audio signal instead of the working system by switchingaccording to judgment by the judging means.
 2. The apparatus for faultdetection for parallelly transmitted audio signals of claim 1, furthercomprising silent and mute detecting means for detecting the audiosignal in small region whether silent or not, comparing the audiosignals of two systems, and detecting whether the silent state is due toa fault or not.
 3. The apparatus for fault detection for parallellytransmitted audio signals of claim 1, further comprising abnormal valuedetecting means for detecting whether the characteristic value extractedby the characteristic value extracting means whether abnormal or not. 4.The apparatus for fault detection for parallelly transmitted audiosignals of claim 1, further comprising converting means for convertingthe input audio signals by converting property of monotonous increase ormonotonous decrease, by keeping or inverting the sign, increasing theabsolute value in the relatively small area of the absolute value, ordecreasing the absolute value in the relatively large area of absolutevalue.
 5. The apparatus for fault detection for parallelly transmittedaudio signals of claim 1, wherein the characteristic amount of said eachsystem is the average of the signal.
 6. The apparatus for faultdetection for parallelly transmitted audio signals of claim 1, whereinthe characteristic amount of said each system is the standard deviationof the signal.
 7. An apparatus for fault detection for parallellytransmitted audio signals, being an apparatus for fault detection forparallelly transmitted audio signals transmitted in channels of twosystems, comprising: characteristic amount extracting means provided ineach system for extracting a characteristic amount in each small regionof each audio signal of each system of said parallely transmitted audiosignals, calculating means for calculating the difference between thecharacteristic amount in faulty region and characteristic amount innormal region in each system if fault occurs in either system and faultyregion by parallelly transmitted audio signals is evident, and faultysystem judging means for judging the system to be faulty at the sidewith the greater difference calculated by the calculating means forfault detection related to redundancy and reliability of the transmittedaudio signals, wherein the two systems comprise a working system and astandby system and the working system sends out the audio signal asoutput audio signal in usual operation and, when the judging meansjudges the occurrence of a fault in the working system, the standbysystem sends out the audio signal as output audio signal instead of theworking system by switching according to judgment by the judging means.8. The apparatus for fault detection for parallelly transmitted audiosignals of claim 7, wherein the faulty system judging means finallyjudges by majority decision process by using plural judging results onthe basis of the difference calculated by the calculating means, andrenders the judging result not significant when the differencecalculated by the calculating means is smaller than a specified value.9. The apparatus for fault detection for parallelly transmitted audiosignals of claim 7, further comprising silent and mute detecting meansfor detecting the audio signal in small region whether silent or not,comparing the audio signals of two systems, and detecting whether thesilent state is due to a fault or not.
 10. The apparatus for faultdetection for parallelly transmitted audio signals of claim 7, furthercomprising abnormal value detecting means for detecting whether thecharacteristic value extracted by the characteristic value extractingmeans whether abnormal or not.
 11. The apparatus for fault detection forparallelly transmitted audio signals of claim 7, further comprisingconverting means for converting the input audio signals by convertingproperty of monotonous increase or monotonous decrease, by keeping orinverting the sign, increasing the absolute value in the relativelysmall area of the absolute value, or decreasing the absolute value inthe relatively large area of the absolute value.